1. Field of the Invention
The present invention relates to an image forming apparatus and a fixing apparatus, and more particularly to an image forming apparatus and a fixing apparatus for fixing a toner image on a recording medium by using a belt.
2. Description of the Background Art
Background image forming apparatuses, such as copiers, facsimiles, and printers, generally include a fixing unit for fixing a toner image transferred on a recording medium such as paper.
One example of the fixing unit includes a pair of rollers, i.e., a heating roller and a pressure roller opposing to each other. A recording medium having a toner image is conveyed through a nip formed between the heating roller and the pressure roller. Heat applied by the heating roller and pressure applied by the pressure roller melt and fix the toner image on the recording medium.
Another example of the fixing unit includes the pressure roller, a fixing belt replacing the heating roller of the above example, and a pair of rollers for rotating the fixing belt. The fixing belt is looped over the pair of rollers. One of the rollers opposes the pressure roller via the fixing belt. The other roller includes a heater for heating the fixing belt from its inner circumferential surface and the pressure roller includes a second heater for heating the fixing belt from an outer circumferential surface thereof. The fixing belt can be heated more quickly than the heating roller of the above example due to its smaller volume and heat capacity. Thus, this fixing unit can be heated to a predetermined temperature more quickly than the above fixing unit including the heating roller after the image forming apparatus is powered on. The two heaters respectively heat the inner and outer circumferential surfaces of the fixing belt, resulting in a quick increase in temperature of the fixing belt.
The image forming apparatus including the fixing belt may use an SPR-C toner. The SPR-C toner is produced by dissolving or dispersing a prepolymer including a modified polyester resin, a compound to perform an elongation or cross-linking reaction with the prepolymer, and a toner constituent in an organic solvent to obtain a dissolved or dispersed liquid, cross-linking and/or elongating the dissolved or dispersed liquid in an aqueous medium to obtain a dispersion liquid, and removing a solvent from the dispersion liquid.
When the SPR-C toner is used in the fixing unit including the fixing belt and the pressure roller, the outer circumferential surface of the fixing belt may be charged and may attract toner particles from the recording medium. This is called an electrostatic offset.
When the electrostatic offset occurs, the attracted toner particles may be transferred onto another recording medium after the fixing belt rotates for one cycle and may form an afterimage on the recording medium. To prevent this, a cleaning member (e.g., a cleaning roller) is disposed to contact the fixing belt to remove the attracted toner particles from the fixing belt. However, when a large amount of toner particles is adhered to the cleaning member, the toner particles may melt onto the fixing belt, resulting in staining and damaging the recording medium.